Investigation of the Effects of Compressibility on Profile Pressure Losses in Axial Turbine Cascades

An improved wind tunnel control system based on Mach number has been developed. Compared with the previous control system, the new system gives improved control of the Mach number, shorter settling times, and allows the wind tunnel to run stably at Mach numbers as low as 0.1. Experiments and computations were performed at the midspan of a turbine cascade. The experiments were run at Mach numbers from 0.2 to 1.00 with corresponding Reynolds numbers of 155,000 to 831,000. The results indicate that the effect of both the Reynolds number and Mach number on the total pressure losses have a similar magnitude for the range studied. The Reynolds number effects on losses are attributed to changes in the boundary layers. The effects of Mach number on the losses are attributed both to the change in the transition location and the change in the loading distribution. The results were combined with data from the literature to evaluate the Reynolds number and compressibility corrections in the Kacker and Okapuu loss system. A tentative Reynolds number correction is suggested based on the computational results. Also, it is suggested that the shock losses will affect the losses before an exit Mach number of 1.0.

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